The present invention relates to a motor brake for an air-compressing internal combustion engine, and includes a hydraulic linkage system disposed between a cam and an exhaust valve, with the hydraulic linkage system communicating via a connecting line with an external regulating mechanism and a leakage oil compensation means of an engine lubricating-oil circuit, and with a butterfly or control valve means being provided that is disposed in an exhaust manifold of the engine and that upon actuation of the motor brake partially closes off the exhaust manifold along with activation of the regulating mechanism.
DE-OS 30 26 529 discloses a motor brake of this general type where a hydraulic linkage system is provided between a cam and a push rod of an exhaust valve of an air-compressing internal combustion engine. The hydraulic linkage system comprises a valve tappet that at the same time is embodied as a cylinder. This cylinder accommodates a piston that cooperates with the push rod. The cylinder space between the piston and the cylinder communicates with a regulating mechanism that is in the form of a piston pump and can, for example, be driven by a cam shaft. The stroke of the piston in the cylinder is limited in such a way that when the valve tappet rests upon the base circle of the cam, and by imparting a pressure from the piston pump, the exhaust valve just opens far enough that in the motor braking operation, during the compression phase, air is released. During the normal exhaust phase, there is no pressure in the cylinder space and the exhaust valve is opened merely by having the tappet run up on a cam. Since there is no pressure on the cylinder space during the exhaust phase, the force of the valve tappet is transferred directly to the push rod by having the piston strike the base of the cylinder. In order to be able to compensate for leakage oil losses of the hydraulic linkage system, the cylinder can be connected with a lubricating-oil circuit via a relief valve.
Such an operation of the exhaust valve has the drawback that the piston pump that is required for this purpose is relatively expensive and is subject to wear. Due to the complicated construction, the mechanism is also susceptible to problems.
DE-OS 33 00 763 proposes connecting the cylinder space of the piston, which cooperates with the cam shaft, to a controllable valve via a line, so that the transfer of the movement of the piston to a valve piston can be interrupted whenever desired. To replenish leakage oil-loses, the hydraulic linkage system can again be connected to the lubricating-oil circuit via a relief valve. A hydraulic linkage system of this type requires a large amount of space, since the cylinder and piston do not form a particularly compact unit. The shortcoming of this unit is that a connecting line, even if it is only a short one, is required between the cylinder spaces; this gives rise to a long time lag.
German Patent Application P 39 39 934 proposes disposing a hydraulic linkage system between a camshaft and an exhaust valve, with the camshaft having two projections. A first projection serves in the customary manner for opening the exhaust valve in the exhaust phase. A second projection can also lift the exhaust valve in the compression phase in order via a pressure-regulating effect to perform braking work. The switchover from normal operation to braking operation is effected by activating a lifting magnet that branches off from a connecting line of the pistons of the hydraulic linkage system. During the time interval in which the lifting magnet is closed, the second projection of the cam can transmit its movement to the exhaust valve, so that this valve can also be lifted somewhat during the compression phase and via exhaust work can perform braking work. Leakage oil loses are replaced from the lubricating-oil circuit via a relief valve. Due to the fact that the piston that is actuated by the cam, and the piston of the exhaust valve, are separated from one another and are connected via a longer line, this valve actuation has a somewhat complicated structure. Furthermore, due to the long connecting line, the valve operation becomes sluggish, i.e. has a time lag, which restricts its use in high speed engines.
Starting with a motor brake of the aforementioned type, it is an object of the present invention to eliminate the pump, which is expensive and susceptible to problems, and to make the control of the exhaust valve during the braking operation more flexible via a modern electronic mechanism.